haystack auxiliary radar (hax) millstone hill radar … auxiliary radar (hax) millstone hill radar...

$: Haystack Auxiliary Radar (HAX) Millstone Hill Radar … Auxiliary Radar (HAX) Millstone Hill Radar (MHR) OUTLINE More history Index of Refraction More basic radar . MIT Haystack Observatory$
MIT Haystack Observatory Haystack 2003-1

AJC 7/20/11

Haystack Radar (HY)

Haystack Auxiliary Radar (HAX)

Millstone Hill Radar (MHR)

OUTLINE

More history Index of Refraction More basic radar


AJC 7/20/11

It is frequently said that, although the atomic bomb ended World War II, it was

radar that won the war.


AJC 7/20/11

MIT Radiation Laboratory •  The primary technical barrier to developing UHF systems was the lack of a usable source for generating high-power microwaves. •  In February 1940, John Randall and Harry Boot at Birmingham University in the UK built a resonant cavity magnetron. •  Bombing of London Sept 1940 – May 1941 (The Blitz) •  Britain was interested in developing practical applications for airborne microwave radar, but did not have the large-scale manufacturing ability to mass produce magnetrons. •  In1940, Britain partnered with the US National Defense Research Committee (NDRC) • 


AJC 7/20/11

MIT Radiation Laboratory

Over the course of five years, MIT researchers designed 50 percent of the radar used in World War II and invented over 100 different

radar systems.

Including: •  Airborne bombing radars •  Shipboard search radars •  Harbor and coastal defense radars •  Interrogate-friend-or-foe beacon systems •  Long-range navigation (LORAN) system •  Critical contributions of the Radiation Laboratory were:

–  the microwave early-warning (MEW) radars, which effectively nullified the V-1 threat to London, and

–  air-to-surface vessel (ASV) radars, which turned the tide on the U-boat threat to Allied shipping.


AJC 7/20/11

Millstone

The BMEWS Prototype

Millstone Radar 1957

Sputnik A-Scope Trace

Transmitter Pulse

Echo

Range

Am

plitu

de

First in Space Surveillance


AJC 7/20/11

Outline

•  More History •  Index of Refraction •  More Basic Radar

Appleton - Hartree

but also …


AJC 7/20/11

Radar Range Measurement

Target

•  Target range = cτ 2

where c = speed of light τ = round trip time


AJC 7/20/11

Phase Velocity, Group Velocity, Index of Refraction


AJC 7/20/11

Illustration of Atmospheric Effects

Elevation Refraction Range Delay


AJC 7/20/11


AJC 7/20/11

Outline

•  More History •  Index of Refraction •  More Basic Radar


AJC 7/20/11

RADAR RAdio Detection And Ranging

Radar observables: •  Target range •  Target angles (azimuth & elevation) •  Target size (radar cross section) •  Target speed (Doppler) •  Target features (imaging)

Antenna

Transmitted Pulse

Target Cross

Section

Propagation

Reflected Pulse

(“echo”)


AJC 7/20/11

Radar Block Diagram

Transmitter

Pulse Compression

Recording

Receiver

Tracking & Parameter

Estimation

Console / Display

Antenna

Propagation Medium

Target Cross

Section Doppler Processing A / D

Waveform Generator

Detection

Signal Processor

Main Computer


AJC 7/20/11

Radar Range Equation

R

Transmitted Pulse

Received Pulse

Received Signal Energy

Transmit Power

Transmit Gain

Spread Factor

Target RCS

Spread Factor

Receive Aperture

Dwell Time

Target Cross Section σ

Antenna Aperture A Transmit Power PT

PT 4πA λ2 4πR2

1 σ 4πR2

1 A τ

Losses

L 1

=


AJC 7/20/11

Pulsed Radar Terminology and Concepts

Pow

er

Duty cycle =

Average power = Peak power * Duty cycle

Peak

pow

er

Time

Pulse length

Pulse repetition interval (PRI)

Pulse length Pulse repetition interval

Pulse repetition frequency (PRF) = 1/(PRI)

Continuous wave (CW) radar: Duty cycle = 100% (always on)

Target Return

1 Mwatt

100 kWatt

10%

100 µsec

1 msec

1 kHz

1 µwatt


AJC 7/20/11

Radar Waveforms

Waves?

or Pulses?

Waves, modulated by “on-off” action of

pulse envelope

What do radars transmit?


AJC 7/20/11

Properties of Waves Relationship Between Frequency and Wavelength

Speed of light, c c = 3x108 m/sec = 300,000,000 m/sec

λ

Frequency (1/s) = Speed of light (m/s) Wavelength λ (m)

Examples: Frequency Wavelength 100 MHz 3 m

1 GHz 30 cm 3 GHz 10 cm

10 GHz 3 cm


AJC 7/20/11

Properties of Waves Phase and Amplitude

Amplitude (volts)

Phase, θ

90° phase offset

A

Amplitude (volts)

Phase, θ

A


AJC 7/20/11

Properties of Waves Constructive vs. Destructive Addition

Σ

Constructive (in phase)

Destructive (180° out of phase)

Σ

Partially Constructive (somewhat out of phase)

Σ

Σ

Non-coherent signals (noise)


AJC 7/20/11

Polarization

x

y Electric Field

Magnetic Field

Electromagnetic Wave

x

y

z E

Horizontal Polarization

Electric Field

Magnetic Field

Electromagnetic Wave

x

y

z

E

Vertical Polarization


AJC 7/20/11

Doppler Effect


AJC 7/20/11

Doppler Shift Concept

c v

λ λ = c f

c v

λ f = c λ

c

λ’

f’ = f ± (2v/λ) Doppler shift


AJC 7/20/11

Resolving Doppler

Tx signal: cos(2πfot) Doppler shifted: cos[2π(fo+ fD)t]

Multiply by cos(2πfot) -> Low pass filter -> cos(2πfDt)

BUT, the sign of fD is lost (cosine is an even function)

So, instead use exp(j2πfDt) = cos(2πfDt) + jsin(2πfDt)

Generate this signal by mixing cos and sin via two oscillators (same frequency, 90o out of phase)

Components are called I (In phase) and Q (Quadrature): Aexp(j2πfDt) = I + jQ

haystack auxiliary radar (hax) millstone hill radar … auxiliary radar (hax) millstone hill radar...

Documents